The present invention relates to a downhole packer. More particularly, the present invention relates to a packer which can be used for downhole testing.
It is important to determine whether there are any cracks, gaps or other irregularities in the lining of a well bore, or in the cement between tubulars which line a well bore, which may allow the ingress of well bore fluid into the annulus of the bore. It is also important that any irregularities in the well bore casing connections and cement bonds are identified and monitored to prevent contamination of the well bore contents.
It is normally difficult to determine whether there are any irregularities in the well bore casing connections and cement bonds as the hydrostatic pressure created by drilling fluid within the well bore prevents well bore fluid from entering the annulus of the bore. In order to overcome this difficulty it is known to the art to use downhole packers to seal off sections of a pre-formed well bore in order to test the integrity of the particular section of bore. One test carried out to identify any such irregularities is a so-called “in-flow” or “negative” test
During an in-flow test a packer is included on a work string and run into a bore. The individual packer elements of the packer tool are expanded to seal the annulus between the well tubing and the well bore, and between the well tubing and tool in the well bore. Expansion or “setting” of the packer, is usually achieved by rotating the tool relative to the work string and prevents the normal flow of drilling fluid in the annulus between the work string and well bore tubular. A lower density fluid is then circulated within the work string which reduces the hydrostatic pressure within the pipe. As a consequence of the drop in hydrostatic pressure, well bore fluid can flow through any cracks or irregularities in the lining of the well bore into the annulus of the bore. If this occurs, the flow of well bore fluid into the bore results in an increase in pressure which can be monitored. As a result it is possible to locate areas where fluid can pass into the well bore through irregularities in the structure of the bore and where repair of the lining may be required. After testing, the bore may be “pressured up” to remove the well bore fluid from the bore and a heavy drilling fluid can be passed through the string to return the hydrostatic pressure to normal.
A disadvantage with conventional packer tools lies in the fact that they are usually set by a relative rotation within the well bore. It is therefore difficult to run other downhole tools which are also set by rotation methods, for example in J-slots, on the work string containing the packer, at the same time as it is difficult to selectively activate one tool at a time. Rotation of the work string in order to activate a well clean up tool or reamer would set the packer prematurely. Therefore historically, it has been necessary to run a separate trip into the well bore in order to carry out a pressure test or in-flow test. As a consequence it is necessary to perform more than one trip down the well in order to clean the bore and monitor the downhole conditions. It will be appreciated that at the considerable depths reached during oil and gas production, the time taken to implement several trips and complex retrieval procedures to recover a work string can be very long. This is particularly true when it is desirable to test the “liner lap” or liner top areas of a well bore. It would therefore be an advantage to provide a packer which can be set by a method other than rotation and can therefore be used in conjunction with other downhole tools on the same drill string.
A further disadvantage with conventional packer tools is that they tend to have large outer diameters. This limits the bypass for circulation of fluid through the well bore and the tool itself when the packer is not set, thereby detrimentally affecting lubrication of the tool and removal of any debris or cuttings from the bore. Furthermore, the fluid circulating around a packer tool within a well bore is often at very high speed due to the limited by pass area. As the only passage for fluid is between the external surface of the packer and the internal surface of the well bore in conventional packer tools, a high flow rate may damage the individual packer elements which are typically located on the external surface of the tool. It would therefore be an advantage to provide a packer tool which will allow high rates of circulation to be passed through a bore without damaging the packer elements of the tool.
It is an object of the present invention to provide an improved method of setting packers within a well bore. A further object is to provide a packing tool which can be run into a well bore simultaneously with other well clean-up tools.
It is a further object of the present invention to provide a packing tool which does not detrimentally affect the normal circulation of fluid within a well bore as it is being run into the bore. A further linked object is to provide a packer tool which allows high rates of circulation to be passed through the bore without damage to the packer elements of the tool.